Harmonics MCPQG Ieee 2005
Harmonics MCPQG Ieee 2005
Harmonics MCPQG Ieee 2005
Harmonic Distortion from Harmonic Distortion from Variable Frequency Drives Variable Frequency Drives
Harmonics
Introduction to Harmonics Symptoms Expected Harmonics from VFDs Harmonic Resonance Understanding IEEE519-1992 Harmonic Solutions for VFDs
Harmonic Distortion
Harmonic problems are becoming more apparent because more harmonic producing equipment is being applied to power systems
VFDs Electronic Ballasts UPS
Effective Grounding
Additionally, in many cases, these electronic based devices can also be more sensitive to harmonics
Harmonic Solutions
Surge Solutions
Harmonic Symptoms/Concerns
Equipment Failure and Misoperation
Notching (electronic control malfunctioning, regulator misoperation) Overheating/Failure (transformers, motors, cables/neutral) Nuisance Operation (fuses, breakers, PC lock-ups) Insulation deterioration Capacitor resonance / failure
Economic Considerations
Oversizing neutrals, transformers, generators Losses/Inefficiencies/PF Penalties Inconsistent meter reading
Expected Harmonics
Source
6 Pulse Drive/Rectifier 12 Pulse Drive/Rectifier 18 Pulse Drive
Typical Harmonics*
5, 7, 11, 13, 17, 19 11, 13, 23, 25 17, 19, 35, 37
Switch-Mode Power Supply 3, 5, 7, 9, 11, 13 Fluorescent Lights Arcing Devices Transformer Energization H = NP+/-1 i.e. 6 Pulse Drive - 5, 7, 11, 13, 17, 19, 3, 5, 7, 9, 11, 13 2, 3, 4, 5, 7... 2, 3, 4
Harmonic Spectrum
Harmonic magnitude (per unit)
0.2 0.14 0.09 0.07 0.06 0.05
Fund
5th
7th
11th
13th
17th
19th
Harmonic Spectrum
If the harmonic spectrum exhibits abnormal magnitudes, it is a good sign of harmonic resonance Typically caused by interaction with Power Factor Correction Capacitors
500
500 450
Capacitor Size
400
400 350
300
300 250
200 100
0 0
0 5 10 15 20 25 Harmonic Order
PCC
(Utility Side)
Possible POAs (Customer Side) Source A Source B MCC-1 AFD XFMR AFD ??? ??? AFD ??? MCC-2 AFD
???
Harmonic Calculators
Voltage Distortion
Current Distortion
Current distortion limits are dependent on the stiffness of the source (Isc/IL)
A stiffer source has lower impedance = more distortion allowed A softer source (i.e. generator) has higher impedance = less distortion allowed
Current distortion limits are typically much more difficult to reach than Voltage distortion limits
T
1>
THD = 80% Is this acceptable? Depends on system full load, % linear load, etc.
The greater the amount of Linear load, the less of an issue the current distortion becomes Looks at the full capacity of the system
If non-linear loads are a small % of the full system current demand, the TDD is less
TDD vs THD
Example: With Harmonic Correction
Total I, rms 936.68 836.70 767.68 592.63 424.53 246.58 111.80 Measured Fund I, Harm I, rms rms THD(I) 936.00 35.57 3.8% 836.00 34.28 4.1% 767.00 32.21 4.2% 592.00 27.23 4.6% 424.00 21.20 5.0% 246.00 16.97 6.9% 111.00 13.32 12.0%
Full load
Harmonic Solutions
Oversized Generator
Xs
for VFDs
480 V
Line Reactor
Isolation Transformer
Active Filter
Blocking Filter 12 / 18 Pulse
Phase Shift Transformers
XT
M M
Tuned Filter
M + M M
Harmonic Solutions
Line Reactors K-Rated / Drive Isolation Transformers
for VFDs
Harmonic Mitigating Transformers/Phase Shifting 12-Pulse Converter 18-Pulse Converter Passive Parallel Tuned Filters Passive Series Tuned Filters Active Filters Active Rectifier (Regenerative VFDs)
Line Reactors
Line Reactor = Inductor An inductor slows down the rate of rise of current.
Current Current
XL = 2fL
Z = R + XL
2
where:
Current - % of Fundamental
80%
60%
40%
20%
0% 1 3 5 7 9 11 13 15 17 19
Harmonic Order
Disadvantages
May require larger enclosure / separate mounting Harmonic reduction may not be sufficient Possible voltage drop issues Produce heat
Advantages
Moderate reduction in harmonics Isolation from Ground Moderate cost (compared to some other attenuation methods)
Disadvantages
Large footprint Separate mounting Harmonic reduction may not be sufficient No increased protection for VFD
30
AFC
AFC
AFC
AFC
Almost complete cancellation of 5th and 7th harmonics Insensitive to system changes
Disadvantages Cost varies Increased size and weight More complexity Current distortion is load dependent Doesnt guarantee compliance with IEEE 519
Disadvantages
Higher Cost Must be applied to each VFD Increased size and weight More complexity
Almost complete cancellation of 5th, 7th, 11th, and 13th harmonics Insensitive to system changes
Multi-Pulse VFDs
6-pulse converter
25% - 40% Current THD
12-pulse converter
18-pulse converter
3% - 4% Current THD
UTILITY
FEED XFMR.
AC DRIVE
5th Filter
7th Filter
Consists of LC combinations tuned to a specific frequency (Typically the 5th or 7th) Act as a shunt (or trap) for harmonics Applied close to harmonic generating loads
Active Filters
Load(s) Source XFMR Typical CT Placement
Alternate CT Placement
HCU HCU
Actively senses harmonics Injects equal and opposite currents to cancel harmonic currents Multiple units operate in parallel to get additional capacity Can also use extra capacity to correct power factor
Active Filters
Power Schematic
Active Filters
Integration into Motor Control Center
Active Filters
Source side Harmonics Attenuated Load side Harmonics Present
Sensitive loads
Active Filters
Active Filters
Advantages
Can be sized to guarantee IEEE 519 compliance Shunt design cannot be overloaded Cancels 2nd-50th harmonic Provides 60 Hz reactive current (PF correction) Can be incorporated in MCC to compensate for multiple AFDs Fast response to varying loads Expandable
MCP
FUSES
+ Bus -Bus
Line filter
Active front end rectifier IGBT devices replace diode in rectifier High frequency switching Supplies forward power to DC bus drive system Regenerates excess power back to the 3-phase AC line with sinusoidal input currents
Regenerative VFDs
Advantages Creates little harmonic distortion Regenerates excess power back to AC line Fast response to varying loads
Disadvantages Not widely used Most complex Very expensive solution
More competitive for large regenerative loads
A B C D E F G H I J
6 pulse 6 pulse with 3% reactor 6 pulse with 5% reactor Phase Shifting Transformer 12 Pulse Series Low Pass Filter 18 Pulse Parallel Tuned Filter Active Filter Regenerative active front end
Summary
There are a wide variety of solutions Different solutions are appropriate in different situations Appropriate solutions depend on numerous factors
1. 2. 3. 4. 5. 6. Number of VFDs Redundancy Existing or New Construction Linear load Facility type Future growth
Best solution is determined from a complete system analysis considering all available filtering methods
SM